The invention relates generally to circuit arrangements for delivering electrical power to a heating element associated with a vehicular window, such as the windshield. More specifically, the invention concerns an arrangement for delivering one of two available levels of electrical power to a vehicle window heating element.
A number of electrically heated windshield or other vehicle window surface elements have been introduced in the automotive industry for providing for clearing of the window surface by the supply of electrical power thereto. Many such approaches additionally provide for two levels of heater element power--a higher power level for a "de-ice" mode and a lower or normal power level for a "defog" mode. Provisions must be made in all of these arrangements for delivering power from the vehicle's electrical power system.
A typical charging system in a vehicle consists of an alternator and voltage regulator wherein the alternator generates a three-phase alternating current signal which is rectified to direct current by a diode rectifier bridge and applied to the vehicle's battery and electrical loads. The battery voltage is kept within a desired range by the voltage regulator which monitors the battery voltage and adjusts the alternator field current thereby controlling the alternator output and hence the amount of current delivered to the battery and vehicle loads.
Due to the power level required in a typical vehicle window heating operation, special arrangements must be provided between the vehicle power system and the heater element of the window. Such special arrangements typically involve either circuitry utilizing multiple regulators for providing different output levels or relatively heavy alternator and transformer apparatus and complex switching schemes for reconfiguring the automotive power control system depending upon which level of window heating element power is required.